Aromatic polybenzimidazoles are characterized by a high degree of thermal and chemical stability. They may be shaped to form fibers, films, and other articles of wide utility which show resistance to degradation by heat, hydrolytic media and oxidizing media. However, many of the polybenzimidazoles are not easily thermally processable at desirably low enough temperatures and pressures. Unfortunately, the aromatic polybenzimidazoles have relatively high moisture regain, which, although desirable for textile fibers, is undesirable for engineering plastics. In addition, they are rather expensive polymers.
Processes for the preparation of aromatic polybenzimidazoles are described in a number of U.S. patents, e.g., U.S. Pat. Nos. 3,901,855; 4,002,679; 3,433,772; 3,441,640; 3,509,108; 3,526,693; 3,549,603; 3,552,389; 3,619,453; 3,671,491; 3,969,430; and 4,020,142. In addition, a review of the processes for the preparation of aromatic polybenzimidazoles is contained in J. P. Critchley, G. J. Knight and W. W. Wright, Heat-Resistant Polymers--Technologically Useful Materials, Plenum Press, New York (1983), 259-322.
Polyamide-imide polymers and copolymers are known in the art. These materials are generally prepared by the condensation polymerization of trifunctional acid monomers such as the 4-acid chloride of trimellitic anhydride and one or more aromatic diamines. Examples of such polyamide-imide polymers are disclosed in U.S. Pat. Nos. 3,347,828, 3,494,890, 3,661,832, and 3,920,612. These polymers may be characterized as having extremely good high temperature properties (Tg of about 275.degree. C. or higher), good high temperature stability, good tensile strength at high temperatures, good mechanical properties and good chemical resistance. These polyamide-imides are useful as wire enamel coatings, laminates, molded products, films, fibers, impregnating varnishes and in other applications where high thermal stability is required.
One of the problems associated with such polymers is that they exhibit generally poor flow properties, which render them difficult to process, particularly to injection mold or to spin into fibers. These polymers are also relatively hydrophilic and tend to absorb moisture which can affect their clarity, heat stability, processability, and mechanical and electrical properties.
Attempts have been made in the art to improve the flow properties of polyamide-imide polymers. For example, U.S. Pat. No. 4,448,925 discloses including from about 1 to about 10 percent phthalic anhydride into the polymerization recipe to provide polyamide-imide copolymers having improved flow properties. However, this technique for improving flow properties is made at the expense of the heat stability and chemical resistance of the polymer. Yet another method for improving the flow properties of such polymers is to form blends thereof with up to about 10% by weight of a polyamide such as Nylon 6 or Nylon 66, as disclosed in U.S. Pat. No. 4,575,924. Once again however, such an approach to solving the flow problem is made at the expense of the thermal stability and optical clarity of the resultant polymer blend.
The novel polyamide-imides having fluorine-containing linking groups which are used in the blends of this invention are described in detail in commonly assigned U.S. patent application Ser. Nos. 07/316,220, U.S. Pat. No. 4,923,960, "Polyamide-Imide Polymers Having Fluorine-Containing Linking Groups" (Paul N. Chen, Sr. and Rohitkumar H. Vora); U.S. Ser. No. 07/316,254, U.S. Pat. No. 4,963,647, "Polyamide-Imide Polymers Having 12-F Fluorine Linking Groups" (Rohitkumar H. Vora, Paul N. Chen, Sr. and Jeffrey S. Devolve); and U.S. Ser. No. 07/316,380, U.S. Pat. No. 4,954,610, "Polyamide-Imide Polymers Having Fluorine-Containing Linking Groups" (Paul N. Chen, Sr. and Rohitkumar H. Vora), all of which were filed on Feb. 27, 1989; as well as commonly assigned U.S. patent application Ser. No. 07/348,634, U.S. Pat. No. 4,962,183, "Polyimide-Polyamide Polymers Having Fluorine-Containing Linking Groups" (Paul N. Chen, Sr. and Rohitkumar H. Vora), filed May 5, 1989.
In addition to improved flow properties, the polyamide-imides having fluorine-containing linking groups used in the blends of this invention also exhibit improved solubility properties in most organic solvents, improved resistance to attack by chlorinated solvents such as trichloroethylene as compared with polyimides, improved hydrophobic properties as well as excellent thermal properties including resistance to thermooxidative degradation.